Pneumatic tire assemblies can be classified generally as either tube-type, in which a casing confines an inner tube filled with pressurized air, or tubeless, in which a lined casing is sealed to a metal wheel rim with the casing and rim defining the space filled with pressurized air. Tube-type tires are most commonly used for smaller wheels such as motorcycle wheels and bicycle wheels. Tubeless-type tires are most commonly used for automobiles and other larger vehicles.
Several types of sealants for pneumatic inner tubes and tubeless tires are known. The sealants can be generally separated into three categories. The first category includes sealants that form an essentially immobile layer on the inside of the tube or tire. This type of sealant is soft enough in consistency to seal around a puncturing object or flow into a hole left by a puncturing object. However, this type of sealant is not well suited for inner tubes, primarily due to the difficulty in applying the immobile layer of sealant to the inside of an inner tube. This type of sealant is also adhesive in nature, and causes the walls of a deflated inner tube to stick together, unless the surfaces are treated or covered to prevent this.
A second type of sealant includes materials that gel or dry out soon after entering or covering a puncture. This type of sealant is typically placed in a tire or tube after the tire or tube has been punctured. This type of sealant has a short lifetime and is therefore not applicable for permanent additions to tires or tubes. This type of sealant can also cause adhesion between the inside surfaces of a deflated inner tube, as discussed above. Further, there is a substantial likelihood that this type of sealant will permanently clog the air valve of the tube or tire, particularly in bicycle tires that are frequently deaired to adjust the pressure for various riding conditions.
A third type of sealant may be characterized as a "mobile" sealant. Typically, this type of sealant includes fibrous and particulate matter in a carrier fluid. The carrier fluid should not substantially dry, gel, or otherwise change in consistency for long periods of time and the fluids are meant to last for years within the tube. The sealant should be mobile enough to slump to the bottom of the tire when the tire is not rapidly revolving, and mobile enough to distribute evenly around the outer portion of the inside of the tube or tire due to centrifugal forces when the tire revolves rapidly. When the tire is punctured and pressure forces the sealant through a hole that is not too large, the fibers and particulates are swept into the puncture and compact there to form a plug that prevents air loss.
As an alternative, many bicyclists who use some form of flat protection choose either thorn-proof tubes or tire liners. Thorn-proof tubes prevent flats simply by their thickness and often thorn-proof tubes are 4 millimeters or more thick. Therefore, many puncturing objects will not penetrate through both the tire and the tube. However, thorn-proof tubes do not prevent punctures from objects longer than about 6 millimeters and they are also very heavy. It is believed that the majority of cyclists prefer not to use them for these reasons. In addition, the thorn-proof tubes have much greater stiffness which compromises the riding quality of wheels containing them.
Tire liners are tough plastic strips that are placed around the inside of the tire between the tube and the tread area of the tire. Tire liners provide protection from some tire penetrations by way of their toughness, but the main protection from typical tire liners is simply due to the extra thickness they provide. Because tire liners are typically less than 2 millimeters thick at their thickest point, they have a much lower weight penalty than thorn-proof tubes. However, they provide substantially less protection than thorn-proof tubes. Tire liners are also stiff enough to have a detrimental effect on the riding quality of the wheel.
The mobile sealants described above provide a number of advantages over the other types of sealant and the thorn-proof tubes or tire liners. Mobile sealants are believed to be most suitable for use in tubes since they are easily emplaced, and do not cause the inside surfaces of the tube to stick together or, when some sealant escapes through a puncture, cause the tube to adhere to the tire. Also, this type of sealant, insofar as it does not harden, does not have a tendency to permanently clog the air valve. Further, the mobility of this type of sealant has important advantages for sealing particular types of punctures. For example, punctures that occur on the sides of the tube or tire require a sealant mobile enough to reach those areas.
While this type of sealant appears to provide a number of advantages, it is believed that it is currently used by only a small percentage of tire consumers. The present inventors believe that this is because existing sealants of this type are far from satisfactory with regard to small tubes, and bicycle tubes in particular.
One of the problems associated with the sealants of this type is that they are often too viscous to adequately spread around the inside of the tube. Given typical sealant amounts used, the full tread extent of the tire will be protected by the sealant only if the sealant is sufficiently mobile to flow easily around the inside of the tube during normal use. In this regard, the viscosity of the sealant relative to the mass of the sealant is critical. For a given viscosity, a larger mass will be more mobile. The viscosity of a mobile sealant is strongly related to the concentration and composition of fibrous and particulate material contained in the carrier fluid. It is relatively easy to make the mobile sealant less viscous by using a lower concentration of these components. However, merely reducing the concentration of fibers or particulates to achieve sufficient viscosity will greatly reduce the overall effectiveness of the sealant, particularly with respect to use for bicycle tires.
Bicycle tires present problems not associated with tubeless car tires, tubeless car tires being much easier to seal than tubes. One reason is that the rubber in the various layers of the tubeless tire is not under a high level of tension, as is rubber in an inner tube. As a result, a puncture hole in a tubeless tire does not tend to "spring open" as it commonly will in a tube. Also, the thickness of a tubeless tire is much greater than the thickness of a tube.
Bicycle tubes are particularly difficult to seal for a number of reasons. Bicycle tubes are relatively thin and require high inflation pressures, a situation demanding a sealant having outstanding sealing capability. Further, the tire tread area is not completely covered by the volume of sealant typically utilized, due to the round cross-section of bicycle tires. The sealant must also seal very quickly and thoroughly because of the low air volume in bicycle tires, and with very little loss of sealant because of the small mass used. The plug must also bleed very little carrier fluid since a low volume of carrier fluid is emplaced in the tube. These special difficulties are compounded by the need for low viscosity in the sealant due to the small mass of the sealant emplaced.
While both the fibrous and particulate matter in the sealant are involved in initiating and forming the plug in the puncture hole, it is believed that the main role of the particulate matter is to close the spaces between the fibers in the plug. That is, without the particulate matter, the plug would be much more porous. If the pores in the plug are not sufficiently closed off, the plug will bleed excessively. Properly formulated mixes should bleed very little, but it is believed that most presently available commercial mixes bleed too much to be suitable for use in bicycle tubes or other small tires or tubes. Those that do not bleed at a significant rate have carrier fluids that are too viscous to be optimum for bicycle tire use. Finally, a substantial fraction of the fluid carrier mass in bicycle tubes is commonly lost by way of gaseous diffusion through the thin inner tube.
The primary problem in formulating a mobile sealant is that improving one characteristic of the sealant will often worsen other characteristics. For example, improving the mobility of given sealant by using a less viscous carrier fluid will increase the tendency of the fluid to bleed. If the mobility of the sealant is improved by reducing the amount of fibers or particulate matter, the ability of the sealant to plug large holes can be substantially reduced. The present invention overcomes these problems by providing a long-lasting and highly mobile sealant that has an outstanding ability to plug puncture holes and exhibits a very low bleeding rate.